N'aviculaccu.} infitsoht.vl \\t-m.vlcttle3. 489 



Navicula-likc bodies in the same tube ; one, very flelieate and straight 

 kind, evidently a Naimema ; the other the large curved kind. Even 

 to the present moment, I cannot explain this phenomenon, for both 

 sorts were in considerable quantities, and quite fi'ee, and therefore it 

 is difficult to suppose one a parasite." Size l-2300th. 



Genus Homoeocladia (Agardh.) — Compound frond, membranou9, 

 filiform, branched, ti'ansvcrsely wrinkled, composed of gelatinous 

 tubes, containing bundles of linear, elongated, navicular bodies, densely 

 aggregated. 



This genus is included by Kiitzing in his great family NavicxdecR. 

 In Ehrenberg's arrangement, it falls, with Schizonema and other 

 genera, under that section, which he describes as possessing a double 

 envelope. 



H. pumih. — Branches equal, obsolctely jointed, capillary, 

 irregularly divided ; navicular bodies linear, shortened, \\'ith rounded 

 apices (P. 17, f. 37, 38.) Length 1 -408th. In the Adriatic Sea. 



H. moniliformis. — Capillary, arranged in a head (coma, like that of 

 a tree), with slender branches, long and moniliform ; collections of 

 naviculae with wide intervals ; navicula) very long, linear, and 

 obtuse. Length l-276th. Adriatic Sea, Trieste. 



H. anglica. — Umbellate at the base, setaceous, di- or seldom tri- 

 chotoraous ; branches equal, acute at the extremities ; bundles of 

 naviculae closely approximate, naviculse very long, perfectly linear, 

 obtuse ; lateral surfaces transversely striated. Length l-84th. Coasts 

 of England and France. It is brownish when recent, and of an 

 opake olive brown when dry. Frond one to two inches high. 



H. maritima. — Comose, setaceous ; terminal branches corymbose, 

 acute ; fasicles of navicuhe closely set ; navicular very long, narrowly 

 linear, obtuse, transversely striated. Length l-96th to l-8th. On 

 stones in the Gulf of Venice (P. 17, f. 47, 48, 49.) 



H. Arbuscula. — Much branched, branches fasciculate; the lower 

 or.es setaceous, the upper capillary, falsely jointed; naviculae linear, 

 rather wide, but elongated, obtuse, and quite smooth. Length l-7th, 

 Venice. 



H. dilatata. — Much branched, very setaceous, branches pointed, 

 thickened upwards ; in clavate closely set bundles ; naviculae linear, 

 elongated, circular, obtuse. Length l-12th. Trieste. 



K K 



